Mobile electronic instruments that are provided with functions for producing vibrations for informing the user noiselessly that a signal has occurred, such as an incoming message in a communication function, or a signal that is produced at the beginning/end of an operation, such as an alarm function, are well known, where such mobile electronic instruments have built-in vibration actuators.
While there are various types of mechanisms known for vibration actuators, a basic structure wherein a magnet is caused to oscillate in one axial direction, within a cylinder (bobbin) that is wound with a coil, where a movable element is structured by connecting a weight unit to this magnet, and wherein this movable element is supported elastically in one axial direction, is a known structure that is built into small mobile electronic instruments. See, for example, Japanese Unexamined Patent Application Publication No. 2012-16153, and Japanese Unexamined Utility Model Registration Application Publication No. H5-60158.
In the conventional technology set forth in Patent Citation 1, described above, a guide shaft is provided along the direction of vibration, where the guide shaft passes through this movable element and the movable element is oscillated along the guide shaft, to ensure a stable vibration. This conventional technology demonstrates superior performance in terms of vibration stability and drop impact durability, but because it is necessary to form a through hole through which to pass the guide shaft through the magnet and weight unit that structure the movable element, there is a cost involved in machining the hole in the magnet, and the mass of the wage is reduced through the formation of the through hole, making it necessary to increase the diameter or length of the weight unit in order to produce the desired mass.
In contrast, in the conventional technology set forth in the aforementioned Patent Citation 2, the structure is one wherein the movable element is guided by the inner surfaces of a cylinder, without having a guide shaft for guiding the vibration of the movable element in the one axial direction, causing a problem with the production of noise due to the movable element contacting the inner surface of the cylinder. Because the point of the vibration generating function in the mobile electronic instrument is to enable sensing of a vibration instead of informing the user via sound that a signal has arrived, it is preferable for the production of noise at the time of vibration to be kept extremely low.
In the present invention, the handling of such a situation is one example of the problem to be solved. That is, an aspect of the present invention is, for example, to provide a vibration actuator that is able to suppress the production of noise at the time of vibration while enabling the cost of machining a hole in the magnet to be eliminated and enabling a reduction in the size of the weight unit, through the use of a structure that does not have a guide shaft for guiding the vibration in the one axial direction.